A torque meter of this type serves to measure a moment for a shaft such as a rotary shaft or a stationary shaft as center.
Typically, detection of torque is made by detecting a torsional force of the shaft produced by torque or a torsional angle of the shaft changed by torque. As a means for detecting the torsional force, means is known which uses a piezoelectric element for generating an electric charge proportional to the force received. Moreover, a magnetostrictive element, which is an element using a material having magnetic characteristics that change when subject to a force, serves to detect torque as force. On the other hand, as a means for detecting torsional angle, a distortion-gage system and a rotation pulse phase difference system are well known. It can detect a minute torsional angle of the shaft as a minute displacement.
Japanese Unexamined Patent Application 2003-083824 discloses a torque meter. The torque meter includes a plate-like elastic body mounted between a flange provided to a rotary drive unit and a rotary driven structure, and has a plurality of circular holes formed in a torque transfer area. In the torque transfer area, a flange fixing part arranged around a central through hole and having a fastening means with the flange is connected to a base fixing part arranged outside the flange fixing part and having a fastening means for a fixing base of the rotary driven structure. A distortion gauge is bonded on the interior surface of each circular hole to measure distortion due to torque acting on the torque transfer area, thus detecting a driving torque produced on an output shaft.
However, with the torque meter as shown in Japanese Unexamined Patent Application 2003-083824 the rotary shaft and stationary shaft often undergo, besides the aforementioned moment, loads such as a thrust load (axial-direction load), radial load (radial-direction load), bending load, and centrifugal load at the same time.
Therefore, in order to avoid the influence of forces other than torque, a device is needed to prevent the aforementioned torsional force or torsional angle from being affected by those loads.
In order to prevent the influence of forces other than torque, Japanese Unexamined Patent Application 53-106181 proposes that a plurality of sensors are mounted in the differential-sensor structure for torque detection, in which the sensors are added to increase an output with regard to torque, and the sensors are subtracted to reduce an output with regard to changes other than torque.
However, although Japanese Unexamined Patent Application 53-106181 can reduce the influence other than torque by virtue of the actuation structure, influences due to sensor-to-sensor unbalance, structural unbalance, etc. had to be removed to sufficiently reduce the influence, raising a problem of difficulties in the manufacturing process.